Allergy sufferers and those with respiratory conditions are often sensitive to particulate materials in the air. Vacuum cleaners and air cleaner filtration devices seek to remove particulate materials in homes and places of business, requiring filters to trap these particles. Without such filters, vacuum cleaners would simply re-circulate the particulate matter back into the air. Industrial dust collection equipment is required to remove greater proportions of smaller and smaller particles from process air streams due to increasingly stringent regulatory requirements. Gas turbine intake filtration systems also must remove quantities of very small particles as the presence of such particles can cause irreparable damage to turbine blades. The cleanliness of an environment, the health of its occupants, the effectiveness of industrial processes, the maintenance of industrial equipment, and the overall aesthetics of living require that submicron particulate materials be readily removed by filter from an air stream.
In order to achieve submicron particulate removal from air streams passing through such systems, inertial separators tend to simply place a physical barrier in the path of particulate material that is then knocked from the air stream into a collection bin. Paper bag dust collectors are simply filters based on paper filter technologies in a bag form. Such paper bags typically simply fit across the air stream for the purpose of separating particulate from the air stream.
Newer filters have been designed with a collection filter or a flat panel or cylindrical cartridges. In these applications, a HEPA filtering material is used. By definition, HEPA filters remove at least 99.97% of airborne particles 0.3 μm in diameter or larger. Because of their general reliability and high level of performance, HEPA filters are often used to minimize the release of radioactive materials, asbestos, lead, beryllium, and other toxic particulates. In vacuum cleaners, HEPA filters are used for air pollution control. Often HEPA structures include an expanded PTFE (ePTFE), layer with a layer of a melt blown fiber combined in a filter construction, or a cellulose filter paper layer with a layer of melt blown fiber combined in a filter construction. These structures are often cleaned by rapping the filter or by blowing filter cake or particulate from the filter using compressed air streams.
The filtration efficiency and cleanability of newer filters is important. These filters must be able to remove dust and dirt but must be easily cleanable without damage to the filter. Often cleaning dirty filters by rapping the filter on a solid object to dislodge dust and dirt can cause the filter media to fail or can cause multilayered elements to delaminate, thus causing the filter to fail through the formation of a pathway for the dust and dirt through the filter structure. Another failure mode occurs when fine dust particles are trapped into the depth of the filter media, such that the dust cannot be dislodged by typical filter cleaning mechanisms, resulting in reduced vacuum power and shorter filter life.
One example of a dust filter vacuum technology using a fine fiber layer in a vacuum bag is Emig et al., U.S. Pat. No. 6,395,046. One example of a filter cartridge in a wet/dry vacuum using expanded PTFE is Scanlon et al., U.S. Pat. No. 5,783,086. Filter materials, such as scrimmed HEPA media, often have high efficiency but often have short lifetimes and can be degraded through water exposure.
There remains a need for a filter media construction suitable for removing odor while maintaining a lower pressure drop and higher efficiency. Additionally, there exists a need for a filter media construction that provides HEPA efficiency, odor control, and anti-microbial treatment with a single medium to control mold growth in cartridge media.